1. Field of the Invention
This invention relates to a toothbrush comprising a handle made of a relatively rigid plastic material and a multi-component toothbrush head, one component of the head being made of the same material as the handle, the other being comprised of an elastomer. The head is resilient and flexible by virtue of being divided into two or more segments. Each segment is linked to an adjacent segment by means of a flexible joint, which comprises a relatively thin integral bridge or hinge, oriented transversely to the longitudinal axis of the brush, made of the same material as the handle and a slot or groove running from the top or bottom surface of the bridge to the top or bottom surface of the brush, respectively, depending on the placement of the bridge. According to one aspect of the invention, each end of the transversely oriented groove terminates in a flange at its extreme outer edge, and the groove and the flange are filled with a soft elastomer. Due to the presence of the elastomer-filled flange, the multi-component joint is resistant to peel stresses, which are caused by flexing of the hinge in such direction that the flanges flex away from each other as the brush head either straightens due to brushing or is forced to assume a convex shape due to the exertion of excessive brushing pressure In another aspect, the front one-half to one-third of the head is predisposed at what has been determined to be a desirable angle, namely 15.degree., with respect to the rear end of the head, wherein the degree of flex is limited first by the positioning of the bridge such that the upper surface thereof is flush with the upper surface of the head and the groove runs to the bottom or bristle-bearing surface, and second by the selection of elastomers falling within a certain range of Shore A hardness filling the groove.
2. Description of the Prior Art
Toothbrushes with curved or angled bristle tip configurations that offer improved access to hard-to-reach areas such as the lingual surfaces of the front teeth, and behind the rear molars, placing more bristles in contact with the outer surfaces of the front teeth are well known in the art. However, many current brushes which have rigidly mounted bristles and a rigid curved or angled bristle surface exhibit an inherent disadvantage when brushing both flat as well as concave tooth surfaces because placing a curved or angled bristle surface on flat tooth surfaces results in fewer bristles making contact with the teeth. These fewer bristles must support the brushing forces applied through the handle, which will result in premature splaying of the bristles. Some toothbrushes have a "power tip" configuration (elongated rigidly mounted tip bristlcs) which are claimed to have improved access benefit. Such brushes are illustrated in WO 94/09678; GB 304,459; U.S. Pat. No. 1,639,880, and U.S. Pat. No. 4,800,608, the teachings of which are incorporated herein in their entirety.
Thus, while fixed angle heads offer improved access to difficult to reach areas, because of their shortcomings, it would be desirable to have an angled or curved brush head that flexes back to a flattened position when the brush is subjected to typical brushing forces.
Toothbrushes that include heads having pivoting or articulated sections joined together in a variety of constructions, such as by hinged articulated sections are well known in the art.
For example, WO 92/17093, the teachings of which are incorporated herein in their entirety, discloses a toothbrush in which the head is divided by one or more hinge-forming grooves in the side of the head opposite to the bristle-bearing side into at least two segments that are flexibly and resiliently linked to each other and/or to the toothbrush handle. An elastomeric Material fills each such the groove.
WO 96/02165, the teachings of which ire incorporated herein in their entirety, discloses toothbrushes with resilient, flexible heads, certain embodiments of which are similar to those shown in WO 92/17093. One embodiment has a curved head and is formed by an elastomer-covered thin extension of the handle. A second embodiment is flexible due to hinge-forming grooves in both surfaces of the head, with an elastomeric material filling such grooves, but with bristle tips that terminate in a concave profile in the stress-free configuration The head can also flexibly conform to a convex profile during brushing.
WO 97/07707, the teachings of which are incorporated herein in their entirety, discloses a toothbrush in which the flexibility of the head is concentrated in the tip of the head. The head comprises a substantially rigid base region adjoining the handle on one side and a link region on the opposite side which is linked to the flexibly resilient tip end. The link region may comprise an aperture, space or chasm in the head material, which has an elastomeric material wholly or partially filling the aperture, space or chasm. The tip region may be angled to form a "power tip" construction.
U.S. application Ser. No. 08/762,783, U.S. Pat. No. 5,758,383, issued Jun. 2, 1988 the teachings of which are incorporated herein in their entirety, discloses a toothbrush having a flexible head divided into two segments separated, in some embodiments, by a generally T-shaped groove, which, in longitudinal cross section, extends transversely across the upper or top surface of the head.
While the above publications illustrate toothbrushes with heads of varying degrees of flexibility, each of them fails to provide means to limit the degree of flexibility of the head.
It has also been found that in certain segmented toothbrush heads having multi-component joints having both hard plastic and soft elastomer elements, with a groove-creating, elastomer-filled hinge between the segments, there is a considerable amount of stress placed on the joint when it is forced to flex in such a way that adjacent segments are forced to flex away from each other. This stress can cause delamination of the elastomer, beginning at the extreme outer edge of the groove and continuing along the entire surface of the groove leading to failure of the joint. None of the prior art brushes provides means to improve the adhesion of the elastomer to the walls of the groove.